The World's Hardest Logic Puzzle Ever!

This is not really a tutorial, but an exceedingly hard logic puzzle for you to solve. According to the late philosopher and logician George Boolos, who was a great teacher and logician at MIT, the hardest (recreational) logical puzzle is one that was invented by the logician and puzzle-master Raymond Smullyan, and modified slightly by the computer scientist John McCarthy.

Here is the puzzle:

SOLUTION

Here is the TED-Ed video on this puzzle, with a discussion of the solution:

Source: Joe Lau and Jonathan Chan, https://philosophy.hku.hk/think/logic/hardest.php
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